This application is based on Japanese Patent Application No. 2001-43405 filed on Feb. 20, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an ignition system and a control method for an ignition system applied to an internal combustion engine (herein after the internal combustion engine is referred as the engine) being capable of rotating in both of directions, a normal rotation and a reverse rotation.
2. Description of Related Art
Conventionally, small size vehicles, e.g. motorcycle, moped, motor scooter, snowmobiles or the like, have no reverse gear to achieve compactness and light-weight. For the vehicle that cannot select a reverse position, an engine ignition system disclosed in JP-A-11-82270 is known in the art for permitting a reverse movement by rotating the engine in a reverse direction.
According to the ignition system disclosed in the publication, the system includes a rotor that has a tooth covering an angular position of Top Dead Center (TDC) located between a compression stroke and an expansion stroke. The system generates a spark on a spark plug of an engine cylinder indicated when a reference signal of the tooth is detected during an idling phase of the engine. On the other hand, in a stable driving condition, system sets a counter value on a counter or the like when the reference signal of the tooth is detected, and generates a spark on the spark plug when a countdown process for the counter value is finished. The ignition timing on the spark plug is always slightly advanced from the TDC of each cylinder.
According to the ignition system disclosed in JP-A-11-82270, however, since the rotor has only one tooth thereon, the rotor rotates almost full circle from a detection of the reference signal for the target cylinder to a spark in the target cylinder. That is, countdown period is too long. Therefore, ignition timing may shift if an engine rotating speed is changed while the countdown process. It is possible to be shorten a period of time from the reference signal to an ignition, if a length of the tooth in the rotating direction extends. But the length of the tooth could not be extended, because the reference signal is also utilized for an ignition signal of a fixed ignition sequence, e.g. during the idling. Further, it is difficult to manufacture the length of the tooth longer.
It is an object of the present invention to provide an ignition system and a control method for an ignition system which is capable of providing an improved accurate ignition control in both of a normal rotation and a reverse rotation.
According to an embodiment of the present invention described below, calculation indicators are located on a forward side of the position indicator in a normal rotation and a forward side of the position indicator in a reverse rotation. The system begins a calculation, e.g. countdown, when the sensor detects the calculation indicator corresponding to a cylinder to be sparked. The system provides an ignition in the cylinder corresponding to the calculation indicator when the countdown is finished. A calculating time period is shortened since a rotating angle range of the calculation indicator and the cylinder corresponding to the calculation indicator is shortened. It is possible to control the ignition timing of each cylinder accurately, because it is possible to decrease a deviation of the ignition timing even if an engine rotation speed is changed.
In the case that the engine has a plurality of cylinder, a position indicator for one of the cylinder may be a calculation indicator for a next cylinder located on a backward side in the rotating direction.
One of the position indicators may include three or more steps, which are located different intervals to indicate the rotating direction by a ratio of the intervals.
The calculation indicator of each cylinder for the normal rotation and the calculation indicator of each cylinder for the reverse rotation may be located on approximately the same distance from the TDC. It is possible to shorten processing time, because the same calculating process may be used for the normal and reverse rotation, e.g. countdown may be executed based on the same preset counting value.
The position indicator and the calculation indicator may be defined in accordance with each cylinder and the rotating direction.